1. Technical Field
The present invention relates to a valve lifter for an automotive internal combustion engine and a surface treatment method thereof.
2. Background Art
A valve lifter for converting the revolution of a camshaft into a vertical movement is mainly formed of alloy cast iron or carbon steel.
As shown in FIG. 1 and FIG. 2, a valve lifter 20 has a cylindrical structure, and the top surface 21 thereof is always in contact with a camshaft 10 that revolves, thereby being continuously subject to friction. In order to reduce such friction, the surface, in particular, the top surface 21, of the valve lifter 20, is typically subjected to mirror surface finishing, diamond-like carbon (DLC) coating, or CrN (Chromium Nitride) coating.
However, the mirror surface finishing does not provide satisfactory surface roughness. The DLC or CrN coating shows low-friction characteristics. The DLC or CrN coating thus requires a specially designed oil to exhibit optimal low-friction characteristics, as disclosed in US Patent Application Publication No. 2005/0098134.
The above information disclosed in this the Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.